1. Field of the Invention
The present invention relates to an ultraviolet laser-generating device, generating an ultraviolet laser beam or ray to be used for inspection or observation of minute pattern defects, foreign matters, etc., in the fabrications of, such as, semiconductor devices and a flat panel display, representatively, and further relates to a defect inspection apparatus and a method therefor, with using the ultraviolet laser ray obtained therefrom, thereby enabling detection of defects with high resolution, as well as a method for maintenance thereof.
2. Description of Prior Art
For example, circuit patterns formed on the semiconductor devices tends to be fine or minute, more and more, as the technology advance in the high integration thereof. In particular, masks and reticules, used in a process of photolithography for manufacturing of the semiconductor devices, as well as the defects of the patterns on a wafer, on which such as the circuit patterns of those are transcribed through exposure, are required to be detected with such the increasing high resolution. As a method for increasing the resolution, there can be listed up a way of shortening the wavelength of an illumination light from region of visible lights to that of ultraviolet lights. Conventionally, as a light source was used or applied, such as a mercury lamp, a Xenon lamp, etc., and only the light having a required wavelength(s) is/are selected optically from the various bright lines (or emission lines) of the lamp, to be applied thereto.
However, for the bright lines of the lamp, there are problems that it is difficult to compensate chromatic aberrations of an optic system due to wide range or width of the emission spectrum thereof, and that the light source comes to be large in size so as to obtain sufficient intensity of illumination, so that it has a bad or low efficiency, etc. In recent years, an exposure apparatus has been developed, installing a light source, KrF eximer laser of 248 nm in wavelength, as a light source thereof for use in manufacturing of the semiconductors, however there are also problems that the eximer laser ray source comes to be large in size thereof, and that it necessitates a certain countermeasure since it uses a fluorine gas therein, etc. Because of this, as the light source of such the ultraviolet (UV) laser ray other than the above-mentioned, YAG laser beam is converted in the wavelength by means of a non-linear optical crystal, thereby obtaining the third (3rd) high harmonic (355 nm) or the fourth (4th) high harmonic (266 nm) therefrom.
A wavelength converter device, obtaining the UV laser ray in this manner is already known by, such as, Japanese Patent Laying-Open No. Hei 8-6082 (1996) <prior art 1>, Japanese Patent Laying-Open No. Hei 7-15061 (1995) <prior art 2>, Japanese Patent Laying-Open No. Hei 11-64902 (1999) <prior art 3>, and Japanese Patent Laying-Open No. Hei 11-87814 (1999) <prior art 4>.
In the prior art 1 is described the wavelength converter device, comprising: resonance means, being positioned at an exit side of a light emission means for emitting a light having basic wavelength, having a resonance frequency corresponding to a resonance length, which is obtained by setting the length of an optical path, through which the light propagates, as said the resonance length, and a plural number of reflection means for reflecting said light in an inside thereof; a non-linear optical material, being positioned on the optical path of the light propagating through the inside of said resonance means, having an anisotropic property therewith, and for emitting the light being incident thereupon and at least one light converted in wavelength, being different from said light in the wavelength thereof; and an electric field applying means for applying an electric field to said non-linear optical material, so that the resonance frequency of said resonance means is in synchronism with the light of said basic wavelength, thereby generating the UV laser ray.
Also, in the prior art 2 is described the wavelength converter device, comprising: a light source for supplying a laser ray; an optical resonator for resonating a laser ray generated from said light source; a non-linear optical material, being positioned within said optical resonator, for converting the laser ray into a light wave having wavelength which is shorter than that thereof; and an optical system for feeding back said laser ray emitted from said optical resonator to said light source via the optical resonator, again, wherein said optical resonator, said non-linear optical material and said optical system are disposed within a vacuum container.
Also, in the prior art 3 is described the wavelength converter device of an outer resonation type, wherein, in a space defined between a wavelength converter element (for example, a non-linear optical crystal) and an optical member for separation of the laser ray (for example, a mirror having wavelength selectability therewith) is provided a material, which is optically transparent, or it is filled up with air or inactive gas, etc., or is kept into a substantial vacuum condition, so as to cut off or insulate a portion defined between said wavelength converter element and the optical member for separation of the laser beam, from an outside, thereby preventing dusts and/or gas components from adhering and/or deposing on a light emission surface for the laser ray of said wavelength converter element and/or a light receiving surface of said optical member for separation of the laser ray.
And, the prior art 4 also describes an extension or prolongation in lifetime of the laser resonator, by removing contaminating materials, such as oil, etc., adhered on the mirror, which constructs the laser resonator, and/or on the component of the non-linear optical crystal, substantially.